Telephone-circuit arrangements.



c. n. LANNING I s. C. DREW. TELEPHONE CIRCUIT ARRANGEMENTS.

APPLICATION FILED AIIG.2, I9II.

Patented Feb. 6, 1917.

3 SHEETS-SHEET I.

Lll.

C. D. LANNING & S. C. DREW.

TELEPHONE CIRCUIT ARRANGEMENTS. APPLlATIoN FILED Aua.2.191|.

Patented Feb. 6, 1917.

s SHEETS-SHEET 2. 9

C. D. LANNING '6A S. C. DREW.

TELEPHONE CIRCUIT ARRANGEMENTS.

3 SHEETS-SHEET 3- Patented Feb. (i, 1917.

APPLICATION FILED AUG.Z, 19H. I.,

...gi l),

CHARLES D. LANNING, ,OF BOSTON,`AND STEPHEN C. DREW, 0F BROOKLINE, MASSA- CH'USETTS, ASSIGNORS TO'CHRLES D. LANNING, 0F BOSTON, MASSACHUSETTS.

TELEPHONE-CIRCUIT .ARRJI'CrEIl'IEN'TS.V

maracas. i

Specication of Letters latent.

Patented Feb.. 6, 191W.

Continuation of application Serial No. 374,280, filed May 17, 1907. This application filed August 2, 1911.

, Serial No. 642,009.

To all whom t may concern .i

Be it known that we, CHARLES D. LAN- NING and STEPHEN C. DREW, citizens of the United States, and residents, respectively, of Boston, county of Suffolk, and Broo line, county of Norfolk, State of Massachusetts, `have invented an Improvement 1n Telephone-Circuit Arrangements, of which the following description, in connection with the accompanying drawings, is a speciication, like characters on the drawing `representing like parts.

This invention r'elates to telephone circuit arrangements being particularly concerned with the ,relation of two voice current circuits inductively connected.

While it has broader and more extensive application for illustrative purposes, we have herein disclosed the invention as ap,l plied to a telephone circuit reinforcing ar-. rangement of the kind disclosed in a prior application of Charles D. Lanning, one of the applicants herein, wherein a repeater embodying Aa receiving element and a transmitting element controlled thereby are both serially related to a conductor forming part of a telephone line system.

We have found hat such transformer losses and impairment of desired Wave form as are present in the transformer action of the induction coil embodied in the commercial telephone'transmitting circuit arrangement (and which in substance is employed in most forms of telephone repeating, relaying or reinforcing arrangements) become a marked disadvantage where the telephone current impressed upon the line by the original voice-actuated transmitter apparatus is again employed to energize or control suchV repeating, relaying or reinforcing apparatus; the new current set up by such last mentioned apparatus being the result of an additional transformation action in which the transformation loss and' impairment of the wave form becomes cu mulative with reference to the original loss and impairment in the original transmitter transformer action.l That is, the transformation loss in the repeater apparatus imf pairs the accomplishment of the object'de sired to be attained by such apparatus which is the reinforcing of the line current, or the setting up olf a new line current stronger than the original line current (as Iof transformers or induction coils as ordi-V narily used.

` In 'telephone' transmission the transfoi mer 1s practically universally though' not necessarily in the 'form of an induction coil or a transformer having a non-continuous ferrie magnetic circuit. Such form is preferred because, with the high frequency and varying-value currents employed, hysteresis losses are encountered with other forms of transformers resulting in and of themselves in transformer losses andother effects which impair voice current production and reproduction so that the'ordinary induction coil with the usual rectilinear or noncontinuous core has been found to be the most eiiicienttype of transformer apparatus for such telephonie use.

Such coils are in general wound with the primary portion nearest the core and in cylindrical layers extending continuously along the core and with the secondary wound in cylindrical layers outside the primary though the secondary is sometimes Wound in sections, inthe well known manner.

In these forms wehave found that there is a clear loss of transformation efiiciency due to the fact that part -of the flux set up by the primary through the core completes its circuit eXteriorly of the core in the space between the4 primary and secondary Windings, thus being ineffective as'regards inductional effects upon the secondary. Moreover this portion of the flux acts with a distinct choking eect, that is, a self inductive effect, upon the primary; and thus acts to prevent completely responsive action of the primary with reference to the variations impressed upon it.

To wholly or materially overcome or so constructed and have put both the usual primary and the usual secondary in series as the secondary winding, utilizing the usual coarse wire interior portion as a primary winding, speaking with reference to,

step-up transformers; similarly positioned and constructed windings being preferably -used and reversely connected for step-down with step-up apparatus places that portionV of the secondary Whichonstitutes the primary within the outer limits of the primary winding and thereby renders the entire flux set up by the primary operative inductionally upon that portion at least of the secondary. With step-down apparatus it places the whole secondary within the outer limits of the primary. This wholly, or to a very great degree minimizes the transformer loss resulting from coils or induction apparatus as ordinarily wound and employed in'telephonic practice and makes the entire flux variation operative upon the secondary and wholly or substantially eliminates the self-inductive choking effect in the primary otherwise resulting from the leakage flux as above noted. e y

The problem of securing effective repeating, relaying or reinforcing action upon telephone lines has been one of great diiiculty and has been one of slow solution, but we have found that with well constructed forms of telephone relays or repeaters (particularly when employed in such circuit arrangements as are disclosed in said application of Lanning above referred to or as are disclosed herein) a very marked improvement is had in efficiency of action by repeating, relaying or reinforcing apparatus when transformer construction and circuiting as described herein is employed, the peculiar eliciency of the same as applied to telephone circuits undoubtedly being due to the fact that the telephone voice current is exceedingly complex, varying greatly both in frequency and in amperage. The voice current as originally impressed being of such slight strength the reduction of loss in transformer action both as regards strength of action and accuracy of wave form reproduction is of vital importance.

It will be seen, therefore, that broadly our improvement consists in so constructing transformers or induction ap aratus and arranging the winding of vsuoli apparatus in telephonie use that the magnetic leakage losses and consequent impairment of eiliciency resulting from the present forms of such apparatus employed in telephonie work are largely eliminated. The principles of our invention may, therefore, not only be applied to various forms of transformers or induction apparatus for telephonie purposes relating to repeating, relaying or reinforcing devices, but also to such transformer or induction apparatus for use in combination with the usual voice-actuated transmitter.

The precise form that we have shown herein (that is, an auto-transformer) has particular advantages in that l the entire winding of the transformer apparatus can be placed in series With the line and thus a complete metallic. circuit afforded for the voice current, which circuit has in series with it the entire winding of the transformer apparatus. This results in bringing into the line as partsof a total inductancecreating element thereof all the various inductance-creating elements of the transformers associated therewith; and, in connection with the particular form of circuiting which We have shown herein for illustrativc purposes (embodying a telephone rcinforcing circuit arrangement) creates a line condition which may be called unitary That is, whatever the length of the line may be from terminal station to terminal station, dependent upon what terminal connections are using the line, the latter with all the inductance creating elements embodied in the transmitting, receiving and reinforcing stations is a unit, obviating the necessity for artificially balancing one section of the circuit against another or balancing against each other the line and the reinforcing circuit.

in connection with a telephone circuit having terminal stations and an intermediate reinforcing circuit arrangement serially 'related to the line.

The invention will be best understood by reference to the following description when taken in connection with the accompanying illustration of one specific embodiment thereof While its scope will be more particularlyv pointed outin the appended claims.

In the drawings Figure 1 represents a telephone line with itsterminal stations and two intermediate reinforcing stations each of the latter having a transformer constructed and connected in accordance with our inventions.

Fig. 2 is similar in all respects to Fig. l except that the receiving elements of the reinforcing stations are inductionally connected to the line.

Fig. 3 represents a similar telephone line with .its terminal station and two intermediate reinforcing stations with the primary portion of the reinforcing transformers having a split or divided connection to the line.

4; is similar in all respects to Fig. 3 except that the receiving elements of the re- We have illustrated our invention herein inforcing arrangements are inductionally connected to the line.

Fig. 5 is a similar diagram of the telephone line with its terminal stations, having two intermediate reinforcing arrangements each embodying a transformer, one of the remforcing arrangements being connected to one side of the main line and the other to the opposite side of the main line.

Fig. 6 is a modified circuit arrangement showing a portion of the telephone line, an intermediate station with two reinforcing arrangements thereat related to the main line, and also a speaking and listening stat1 on connected to the line at said intermediate point.

Fig. 7 shows a telephone line with terminal central energy stations, having two intermediate reinforcing arrangements connected to thcI line, eaclrreinforcing arrangement having both its receiving and transmitting elements connected -to the line through a transformer constructed and connected in accordance with our invention, the connections from the respective central energy stations to the terminal speaking and listening stations, and the instruments and connections of the latter being omitted.

Fig. 8 is a sectional view of a transformer in the form of an induction coil constructed and connected in accordance with our invention.

Referring to the figuresin detail it will be seen that there are certain features in common with reference to all the circuit illustrations, that is, Figs. 1 to 7 inclusive. That is, in all said figures the current reinforcing devices embody a receiving element as the magnet 8, in all such figures, there being connected therewith in Figs. 2, 4 6 and 7, a receiving transformer 15; and further embodying a transmitting element operated and controlled by said receiving element as the microphone 9 controlling the circuit energized by the local supply 10 in series with the primary of the transmitting transformer 12.

In all said figures also it will be seen that each of the said receiving' elements and -transmitting elements are connected in series to a conductor and both of them to the same conductor, forming part of the line system; saidconductor in the forms illustrated being one of the main line conductors. That is, having reference to the action and reaction between the line system and the reinforcing arrangement, the latter is inseries relation to a single undivided conductor, this conductor in the special form shown being as stated one of the main line conductors. The general advantages of this construction and 'circuiting are fully set out in said application of said Lanning, being in brief that all weakening and contiict of currents is avoided through the elimination of reciprocally arranged main circuit portions and the elimination of forms including bridge conductors with the one portion of the reinforcing arrangement related to the bridge and another portion to another bridge or to a portion of the circuit exterior to the bridge.

By this arrangement as disclosed in said application the reinforcing'arrangement is acted upon by and reacts upon a single and the same conductor. Further in this form of connection and in the special form shown herein and in said other application referred to the reinforcing arrangements are in series relation to'the main line conductor so that the total original line energy is conserved and built up by the reinforcing action without any weakening of the line effects at either terminal station by the interposition of bridge circuits or other form of split or divided main circuits therebetween.

In all these figures thc transmitter elcments of the reinforcing arrangement. whethertlie receiving transformer or thc transmitting transformer thereof. are preferably constructed and connected in thc gcneral manner described in Fig. 8; and are so sistance continuously surrounding the core 30 and placed next thereto and with the balance of the winding 33, composed of relatively fine wire of the desired number of turns and ohmic resistance. surrounding the primary; this fine wire portion may be in a single compact body of turns as shown, or in section form. The whole winding is connected in series, being wound in one direction, the entire winding being used as a secondary and the coarse wire portion as a primary, in step-up work.

Preferably when employed as a step-down transformer, as in connection with the receiving elements of the reinforcing stations in Fig. 7, the transformer is wound in the same way and the entire winding used as a primary with the coarse wire winding used as a secondary.

Whateyerithe type of the transformer. that is, whether induction coil or other form we embody the principle illustrated in this construction, that is, so arrange the windings and so connect them that a portion at least of the step-up transformer type secondary winding is within the outer radial limits of the primary winding; that is, lies Within the space surrounding the core the nlimits of which space inclose the primarv winding. In this manner, as we have pointed out, the leakage loss resulting from passage of flux between the primary and secondary windings is substantially or wholly eliminated; and the result of this elimination is not onlyr to increase the strength of the induction action upon the secondary but to relieve'the primary of the choking effect otherwise resulting from this leakage flux. This construction we find to be of great advantage in all transformer.

transmitting elements of repeating, relaying or reinforcing stations where transformers are used.

With this explanation of the general circuit arrangements and the construction in connection with the tls-'former the detail figures illustrating the general clrcuit arrangements will be clearly understood.

'In Fig. 1 A and B designate in general the terminal stations and 1 and 2 the main line connecting-the same. Two reinforcing stations are shown both of which are connected to the conductor forming part of the main line system-in the same manner and a description 'of one will suiice. The main line is-in series with the electro magnet 8 which diagrammatically represents any of the usual type of initially energized telephonic receiving magnets. The line then passes in series through lthe condenser 14 and the whole Winding of the transformer 12 constructed and connected in detail as shown in Fig. 8 and as above described. 9. represents ldiagrammatically any of the usual forms of variable resistance mlcrophone having its vibratory electrode connected to an armature in the field of the receiving magnet 8, said microphonehaving in series the primary portion of the transformer 12 and a local source of energy 10.

By this means voice-caused currents impressed upon the line by either of the terminal stations energize the magnet -8 which in turn by its effect upon the vvibratory electrode of the microphone 9 sets up current variations in the local circuit in series with the transformer primary again inducing alternating currents harmonious lwith the original voice-caused lcurrents which are added to the original mainline current.

It will thus be seen that the new alternat-- ing current set -up by the-reinforcing ar rangement iscausedby the-series action of a. conductor forming part of the line system and again sets up by series action upon said conductor another and' harmonious alternating current. It is obvious, of course,'that the connections of the reinforcing arrangement of the line should be such thatthe new current -set up .by the reinforcing inl struments shall be harmonious in phase with the alternating current originally impressed upon the line by the terminal station. If this is done and synchronism of the two current effects maintained, cumulative rein forcement of the voice current on the line vwilly be had,.tl 1e full strength of the original current being retainedon the line subject only to the slight energy loss required to operate the reinforcing instrument. l

` The construction shown.' wherein the4 reinforcing instruments are serially related to one of the main line conductors is the -preff erable form, although other circuit relations of the receiving and transmitting elements might be employed; but ,the connections shown in Fig. 1 illustrate in general the preferable form of connection, avoiding as it Adoes the" weakening of the line current effects by bridging or other form ofsplit circuit arrangement. i.

This general form is disclosedpin the said application of said Lanning above `referred by reason of the vimproved construction and connection of the transformer an added efboth the receiving and transmitting element of the reinforcing station and it will .further be seen that the total .inductional effect of the transformer 12 is delivered onto themain line, the inductional choking effect that lwould otherwise become operative upon the insulated primary of thetransformer Vbeing obviated; this inductive-choking effect arising principally, itwill be clear, upon that portion of the primary that composes the transformer winding, and which therefore is in series with the line.

Due to the relation of the'- primary and secondary portions of the transformer and connections herewith the direct and alternating currents normally tend to be confined to their respective portions, but a condenser may beinter'pOSed as at 14 to check direct current iow in the conductor related to the main line system. As to alternating current flow in the transformer primary this is sub# stantially negligible and moreover we 'have found that varlable resistance microphones Aof the usual type and particularly those of the granular contact type offer in and ofthemselves avery heavy resistance or impedan'ce to alternating current flow, this being caused probably by the multiple current paths through such granular contact micro-v In Fig. 3 the connections of the reinforcing arrangements and the transformers thereof to the line are the same as in Fig. 1 except that the mainline is tapped out of the center of the primary portion of the 'to but in the form illustrated in the drawings Y izo Lafrance transformer winding and, in addition to the connection of the local direct current circuit to the transformer primary, an independent .loop circuit is formed around the primary portion through 117 and the condenser 18 whereby any inductional effect reacting upon the primary portion ,of the transformer may be balanced by opposed induction effects upon the portions thereof, and at the same time the short circuiting of the direct current flow through such loop circuit prevented.-

In Fig. 4 the connections of the reinforcing arrangements and their transformers to the line are the same as in Fig. 3, the receiving elements of the transformer being, however, inductionally connected to the line by the transformers 15 and as in Fig. 2.

In Fig. 5 two reinforcer arrangements are shown, each connected independently to one side ,of the main line circuit in the same manner as is shown for the'connection of the reinforcing arrangement in Fig. 3. By this means reinforcer arrangements are symmetrically placed on the main line circuit so that reinforcing action is symmetrically had thereon, having reference to the length of mainline extending between the terminal stations and alternating current action thereon. It will be understood, of course, that in place of the precise connections shown in Fig. 5 for the reinforcing connections any of the connections herein shown in any of the figuresmay be substituted.

In Fig. 6 two reinforcing arrangements with their transformers connected as described are shown .connected to one side of the main line 1 and 2 at an intermediate point, symmetrically related to a speaking and listening station comprising the transmitter 4.- and receiver 3 -and transmitting induction coil 6.

In Fig. 7 in place of the local energy terminal stations illustrated in Figs. 1, 2, 3, 4 and 5 there is illustrated a line between two central energy lsupply stations B, B, the local `station connection from such central energy station supplies 20, 20 and 21, 21 respectively being indicated but the other connections to the local station instruments being omitted. In this form in connection with the main line 1, 1 between the terminal central energy stations.` are shown two reinforcing arrangements with their transformers, one being connected to one side of the main line and the other to the opposite side as illustrated in Fig. 5. Further in this form the connections of the receiving elements lof each of the reinforcer arrangements are shownas step-down autotransformer connections, the transformer being Wound and connected as a step-down ltransformer in accordance with the principles ofl our invention and as above descrlbed. i

sections; and if properlycircuited so as to Fig. 8 has been described in detail above. The circuit arrangement as herein shown in its detail form for illustrative purposes is, as above stated, an improvement on that disclosed in said co-pending-application of 1 Lanning.

secure phase harmony of the original line current and the reinforcing current and if further so designed as to minimize or eliminate mechanical lag or inertia and maintain synchronism, a unitary action of the whole telephone line, including the reinforcin circuit, is had, eliminating reaction In other Words, synchronism and phase harmony are established and cumulative reinforcing -action had.

By the circuit herein disclosed it will be seen certain improvements are secured tending toward greater efficiency. The induction coil or transformer as specifically illustrated is so circuited as to be in action obviously an auto-transformer. Further, the connections of the line to the reinforcing instrument, as related to the intermediate 4connections of the reinforcing system, are

preferably made lnot only so that the primary and secondary portions of the reinforcing induction coil are connected so as to have a similar magnetizing or inductive effect (i. e., as an auto-transformer) but also so that this inductive' effect` is harmonious (in all alternate current telephony) with the phase ofthe original transmittercaused current. Since the induced current effects in both portionsof the repeater transformer are harmonious or similar in phase, and since the self-induced current in the primary portion of the repeater' transformer is opposed in polarity to the change of current flow of the direct current therein, it results that preferably the voice-caused current and the total repeater or reinforcercaused current are harmonious in phase and thus cumulative in effect but opposed to the change of direct current flow in the primary of the repeater.. i

-()ur investigations show that as a result of this system of crcuiting, the self-induced current of the reinforcer transformer primary winding is delivered on to the main line; and not only delivered onto the main line but Withdrawn from that portion of the reinforcer primary through the local battery and the reinforcer current-varying device. The latter elements are, therefore, relieved of the choking effects of this self-induced current. This is of great benefit in telephone coils because of the fact that the ratio of windings between the primary and secondary in such coils usually is relatively low; z'. e., .the number of turns in the primary is relatively large and hence the self-induction is large. v I

Moreover, when using alternating currents on the line, as is practically universal, a device may be interposed either in the alternating current sections or the direct current sections or both to check the How in the alternating current section of any leakage from the direct current looped sections, or, conversely, to partially .or wholly check the fiow of leakage of alternating currents in the direct current section. We have illustrated, for instance, a condenser in the alternating current sections in looped relation to the reinforcer direct current sections to check any leakage of direct current from the latter into the former. In the same way an asymmetric or unilateral element may be 1nterposed in the direct current sections, so that the leakage flow of one phase of alternating current therein, if such exists, may be checked; or a choke coil of low ohmic resistance but heavy inductance may similarly be interposed in said di-rect current conductors. p

With reference to the unitary .character of the circuiting therein pointed out, the circuit herein ldisclosed accomplishes af further step, for it willv be seenv that the whole main line, including the original 'transmitter induction coil secondary and the receiving and transmitting elements of theA reinforcing instrument are series connection.` In 4this way the capacity. and self-induction elements of the lineand of the reinforcing system make up a unitelement; that is, whatever the line length -may bev or however the length of lineffrom the reinforcing station to terminal station may relatively vary these are qualities of onec'ircuit of which the capacity and inductance of the transmitting coil, of the line, and of the elel ments of the reinforcing instrument are merely component parts ;-and are-not elements of differently constituted and varying circuits and hence requiring adjustable balancing arrangements.

We have lherein shown the repeater transinittery transformer as an auto-transformer having only a portion of its winding in the primary. This it will be clearly apparent to those skilled in the, art is the preferable forni particularly in telephonie, work, as the olimic resistance of the primary is thus reduced, this affecting the direct currentlow therein, and thereby affecting the effective action of the variable resistance device, which action has relation to the total resistance of said primary; and this arrangement of course gives any desired voltage increase.

' thereof.

But obviously the whole winding of the repeater transformer could be placed in series afsf a primary and yet give a reinforcing e ect.

It will be understood that some of the drawings are meant to show broadly -tele.

`cui`ts that ai'e of the central energy type.

Where the circuit is of a central energy type necessarily including (i. e.. operatively reqiiiring) adirect current fiowthrough all portions ofthe main line obviously the condensers in the linewould be omitted as might be appropriate; and as already pointed' out in the specification the difference of potential across the two connections of the repeater loop circuits tothe main line is such that the main line flow through the loop circuitwould bel substantially negligible; while i-eversely the resistance of the main line considered 'as a loop of the repeating circuits will be relatively so great that the flow of current designed to' pass only through the loop circuit will be substan` tially negligible in the main line. v

Wherever in the claims the phrase mag- .netically independent. is used as vapplying 'separateniagnetic cores, or operatively separated windings, so thatenergization of eachsuch coil will directly affect only the desired ,or related instrument -or portion `In the sub-.joined claims where we use the phrase fvoice-cu'rrent circuit we refer to a circuit iii a telephone system wherein varying currents flow, the saine being le- -sigi'ied-to correspond in wave forni with the complex form of wave set up by the voice; as distinguished from ordinary current wave foi-ins such as are used in other branches of alternating current transmission; the latter, of course, being of constant repeated form and a compound of simple alternations,

' whereas the former is not only a compound of main alternations and of alternationsof variations impressed thereon (corresponding to the dominant tones and over-tones in the voice) but varies constantlgY in frequency, as following the voice pitch, and ii'i amperage, as following the voice energy. Iii the claims, therefore, it is this character of circuit, designed to carry this complex current form, and to be related inductionally for transference ofthis wave form, which is designated voice-current circuit.

Without limiting ourselves, therefore, to

the precise forms of apparatus as shown in Lampes the drzwvings Which are employed merely for illustrative purposes what we desire to.

claim broadly as our invention is:

l. In a telephone system in combination trolled by said device, the said transformer being so Wound and constructedy that a portion at least of the secondary Winding lies f within the space limitedby the outer radial limits of the primary winding; the said second mentioned portionof said winding hav ing fixed connections to a direct-current-energized c1rcu1t with a current-varying device therein operatively controlled by said voice-current-energized conductor; the said repeating de'vice being connected to said" system solely for series actuation thereby.

2. In a telephone system in combination with the main line and its terminal instrumentalities, a voice-'current-energized conductor in said system and a voice-current repeating device, said conductor and device being inductionally-connected by a transformer, said transformer having/its Winding composed of an interior portion of coarse wire and an exterior portion of fine wire and having its whole winding in` series with said conductor and a portion in series with anotherl circuit related to said repeatitng device.

3. In combination with a telephone main line system and its terminal instrumentalities, a line-actuated voice-current repeater arrangement comprising a receiving velement and a transmitting element operated thereby, said transmitting element being inductionally connected to said line system by a transformer: said transformer having the interior portion yof windings composed of coarse wire and the balance thereof of relatively fine wire and having its whole winding in series with the line, and said coarse wire portionin series with the related repeater device.

4.*In combination With a telephone line system a voice-current reinforcer arrange-V ment actuated by a voice-current energized conductor in said system and serially related to said conductor and operably related serially only to said conductor, said reinforcer comprisinga receiving element and a transmitting element operated thereby and said transmitting element being inductionally connected to said conductor by a transformer; said transformer having its winding composed of an interior portion of coarse wire and an exterior portion of rela-` tively fine wire and having its Whole winding in series with said conductor and said coarse Wire portion in vseries with the related repeater devices.

5. Ina telephone system, the combination y of a station provided with transmitting and receiving instruments, a metallic circuit connecting the same with another station, a local reinforcing circuit operably related to but one of the sides of said metallic circuit and provided with a battery and a varying resistance medium, in said reinforcing cir,- cult, an lnduction coil energized by the current'undulations of saidrein'forcing circuit, l

the Awindings of said coil being in series with one another and the said side of the metallic circuit and an electromagnet operatively connected with the main line for actuating said resistance medium.

6. In a telephone system, a main line and means for generating current undulations therein, an electromagnet,-in series relation to said line, and a repeating circuit containing a source of electrical energy and a varying resistance medium, the latter operatively related to and-actuated by said electromagnet, and an induction coil, the windings of which are in series with said line, the said electro-magnet and said induction coil being magnetically independent of each other.

7. AIn a telephone system, a. main circuit provided With means for currentv undulations therein and anelectromagnet, an induction coil with its whole winding in selr1es 4wlth'said line, and a local c1rcu1t contions harmonious to those produced by said current generating means are transmitted from said local circuit to said main circuit. l y

8. In a telephone system, the combination with separated stations, of a main line connecting said stations means for producing current undulations therein` and a local circuit in repeating and reinforcing relation to said line, provided with an induction coil having its windings in series with said line, and means actuated by the current undulations of said main line for producing in said local circuitand transmitting to said line, through the action of said induction-coil, current undulations harmonious to the original undulations thereof, the said induction coil being magnetically independent of the controlling means for said local-circuit as actuated by said main line.

9. In a telephone'system, the combination with a main line circuit, of means serially related to but` one side of said circuit for reinforcing the energy undulations thereof,

llO

said means including an induction coil having a split primary with its branches serially connected and in series with the secondary thereof and said main line circuit.

10. A system for the transmission of electrical energy comprising a main line, means for energizing said circuit, a repeating cir,-` cuit connected with said main line, means serially associated with the said main line and controlled by the current variations thereof for producing corresponding current variations in said repeating circuit, and means serially associated with the repeating circuit and said current-variation-producing Ameans for reinforcing' the energy passing through the latter, the said means serially associated with the said main line and the said means serially associated with the' repeating circuit being magnetically independent of each other.

11. A system for the transmission of electrical energy comprising a main line me-f tallic circuit, means for energizing said ci r cuit, a repeating circuitv connected with said main line metallic circuit, means serially associated with said main line metallic circuit and controlled by the current variations thereof for producing corresponding current variations in said repeating circuit, and means serially associated with the repeating circuit and said current-Variation-producing means for reinforcing the energy of the main line circuit passing through the latter.

12. A system for the transmission of electrical energy, comprising a main line circuit, means including a source of electrical energy-for producing 'current undulations therein, an operatively connected repeatmg circuit, means comprising an electromagnet energized by the current undulations of Said main line circuit for causing corresponding current undulations in said. repeating circuit, and means including an induction coil connected with said repeating circuit and haring its primary and secondary windings in series with one another and said main line for transmitting to the main circuit the current undulations of said repeating circuit. 13. A system for the transmission of telephone currents comprising a main line circuit, means for producing telephonic current undulations therein, a loop circuit having its terminals connected to one side of said main line circuit and provided with a current varying device, an induction coil haring primar f and secondary windings in series one with another and said main line, one of said windings being in series with the current varying device of said loop circuit, and electromagnetic means serially related to and energized by the current producing means of said main line circuit for operating said current varying ldevice to produce current variations corresponding to those of the main line in said loop circuit and through the inductive action of induction coil to transmit the same to said main line circuit.

14. In a telephone system, a main line, means for producing current undulations therein, a repeating circuit associated therewith having an independent source of electrical energy and a current varying.device actuated by the current undulations of the main line, and an induction coil provided with a split primary and a secondary winding in series relation to said main line.

15. In a telephone system, a main line, means for producing current undulations therein, repeating circuit associated therewith having an independent source of electrical energy and a current varying device actuated by the current undulations of the main line, and an induction coil provided with a split `primary and a secondary Winding in series relation to said main line, said main line having a condenser for shutting out the battery current of the repeating circuit.

16. In a telephone system, the combination of a main line circuit extending between separated stations, ofmeans for producing current undulations therein and means comprising an electromagnet 8 in series relation with one side of the main circuit, and a repeating circuit comprising a current varying medium 9 actuated by ,said electromagnet, a battery 10 and an induction coil 1Q, the windings of which are in series with the same side of said main circuit, for transmitting thereto, current' undulations proportional and harmonious to the original current undulations therein, said induction coil having a split primary with-its branches in seriesy with one another and with the secondary winding thereof and connected intermediate its ends at the branching point thereof to said line.

1T. ln a telephonic reinforcing circuit, the combination with the main line speaking circuit and its terminal instruments, of a local circuit, a source of electrical energy therefor, means serially related to the main line and adapted to impress on said loca-l circuit current variations harmonious with the original voice-caused currentl influences impressed on the main line circuit, and means also serially related to said main line circuit for producing in the latter current infiuences harmonious with Said current variations of said local circuit, the first and Second mentioned means being magnetically independent of each other.

18. In a telephonic renforcing circuit, the combination with the main line speaking cir cuit and its terminal instruments, of a local circuit, a source of electrical energy therefor, meansserially related'to the main line and adapted to impress on said local circuit current-variations harmonious with the original voice-caused influences impressed on the main line, a local induction coil with its primary and' secondary in series with the said main line and one another.

19. In a telephonie reinforcing circuit, the combination with the main line speaking circuit and its terminal instruments, of a local circuit, a source of electrical energy therefor, means serially related to the main line and adapted to impress on said local circuit current-variations harmonious With the original voice-caused influence impressed on the main line and a local induction coil with its primary in balance split series with its secondary and with the said main line.

20. In a telephonic reinforcing),` circuit, the combination with the main line speaking circuit and its terminal instruments, of a' local circuit, a source of electrical energy therefor, means serially related to the main line and adapted to impress on said local circuit current-variations harmonious with the original voice-caused influences impressed on the main line, a local induction coil with its primary and secondary in series with the said main line and one another, and a condenser interposed in the said main line el;

terorto the said primary and secondary.

2l. In a system for the transmission of electrical energya transmitting and receiving device, a continuous circuit between said devices, means for producing current undulations therein, means energized by said current undulations and in series relation With the main circuit for reimpressing upon the latter current undulations harmonious with those impressed by said current undulationproducing means and means for controlling the effective lag of said reimpressing means.

22. In a telephone system, a sending and receiving station, an auto-transformer and an intermediate voice-current repeater and reinforcing circuit arrangement having connections with the line circuit through said auto-transformer.

In testimony whereof, We have signed our names to this specification, in the presence of tivo subscribing Witnesses.

CHARLES D. LANNING. STEPHEN C. DREW.

Witnesses:

THOMAS B. BOOTH, ROBERT H. KAMMLER. 

